Pneumatic tires and method of making

ABSTRACT

The present invention relates to new and novel tire construction and method of making same wherein the uncured elastomeric material that is laid upon the tire building drum ( 22 ) during building of the tire preform ( 10 ) will not experience subtantially meridional stretch which would otherwise cause a decrease in the uniformity of ply thickness during expansion of the preform in the vulcaninzing mold.

TECHNICAL FIELD

The present invention relates to pneumatic tires and the method ofmaking such tires. More particularly, the present invention relates tothe construction of a preform tire using an inner liner formed of aplurality of overlaying plies.

BACKGROUND OF THE INVENTION

The automotive pneumatic tire is typically made using the flat bandmethod of tire building wherein the various components, or plies, of thetire are applied, as flat stock, upon a rotating tire building drumforming a hollow, barrel shaped preform. In building the preform, theinner liner is first wrapped upon the drum followed by the carcass pliesgenerally containing the tire reinforcement. The carcass plies are thenfollowed by the belt plies, the side wall plies and the tread ply. Thebarrel shaped preform is then removed from the building drum and placedwithin a vulcanizing mold, having the general shape of the finishedtire. The barrel shaped preform is next heated and expanded radiallyoutward into the mold ask periphery typically by directing pressurizedhot gas or steam into a bladder disposed within the preform. During theradial expansion of the preform within the mold, the cylindricallyshaped plies must expand radially outward to radial dimensions muchbeyond those of the original preform. Therefore, the elastomericmaterial of each preform ply must stretchingly expand much like aballoon. During this expansion step the material thickness of thepreform plies may be expected to decrease.

Of particular concern, in the present invention, is the inner liner ply.Typically the inner liner ply is laid upon the building drum as a flatpiece of elastomeric stock having a uniform thickness. Thus, as theinner liner ply expands radially outward during the expansion step, thethickness of the inner liner is stretchingly thinned resulting in aninner liner ply having a thickness that progressively decreases from thetire bead area to the tire crown.

Therefore, to have a given inner liner thickness in the tire crown area,the thickness of the inner liner ply, when laid upon the tire buildingdrum, must be oversized to allow for the stretching of the ply as thepreform is expanded during the expansion step. Accordingly, the typicalautomotive tire structure exhibits an inner liner ply having excessmaterial in the tire bead and side wall areas. Prior art patentapplication WO-A-96 30221 also shows an air-permeation prevention layer(8) with layers (7) extending from ends of a belt (6) toward the center(C).

PRIOR ART

To overcome the above described disadvantage, it has been a practice ofthe prior art to provide an elastomeric sheet having a variablethickness across its lateral width. Such inner liner sheet stockembodies a sheet thickness that progressively increases toward thecenter of the sheet from both sides. Thus, when such sheet stock isradially stretched during the expansion step, stretching occurs in thearea of increased thickness thereby forming an inner liner having anapproximate uniform thickness. However, such specialized sheet stock ismore expensive than the uniform thickness sheet stock to manufacture andis unsuitable for rolling and storing on a feed spool prior to applyingit upon the tire building drum.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and tirepreform structure to eliminate the variable thickness of an automotivepneumatic tire inner liner when built by the flat band method of tirebuilding.

Another object of the present invention is to provide a method andpreform structure which results in a savings of elastomeric material inthe tire inner liner that aids in weight reduction of a given tire.

In accord with the present invention, the standard practice of applyinga single ply of elastomeric material upon the tire building drum to formthe inner liner is replaced, in a first embodiment, by two overlappingplies of elastomeric material each having a uniform thickness. The twooverlapping plies are laid upon the tire building drum such that whenthe tire preform is expanded radially outward during the expansion step,the gauge of the overlapping liners is reduced by stretchingcircumferentially to that necessary to prevent air penetration. Becauseof the minimal meridional (bead to bead) stretch during the expansionstep, a single layer of the liner plies is sufficient.

As an alternative embodiment, the inner liner ply may be made-up of twoseparate elastomeric plies laid upon the building drum in a spacedrelationship to each other with a third ply of elastomeric materialbeing laid thereupon and overlapping the two spaced plies. As with thefirst embodiment, the three overlapping plies are laid upon the tirebuilding drum such that when the tire preform is expanded radiallyoutward during the expansion step, the gauge of the overlapping linersis reduced by stretching circumferentially to that necessary to preventair penetration. Because of the minimal meridional (bead to bead)stretch during the expansion step, a single layer of the three linerplies is sufficient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a cross sectional view of a typical automotive tireconstruction, subsequent to expansion of the preform but beforevulcanization has taken place, embodying the preferred embodiment of thepresent invention;

FIG. 2 presents a schematic perspective illustrating the flat bandmethod of building a tire preform and showing application of the innerliner flat stock to the tire building drum in accord with the presentinvention;

FIG. 3 presents a cross sectional view taken along line 3—3 of FIG. 2showing the inner liner, flat stock plies as laid upon the tire buildingdrum;

FIG. 4 presents a cross sectional view of a typical automotive tireconstruction, subsequent to expansion of the preform but beforevulcanization has taken place, embodying an alternate embodiment of theinvention;

FIG. 5 presents a schematic perspective illustrating the flat bandmethod of building a tire preform and showing application of the innerliner flat stock to the tire building drum in accord with an alternateembodiment of present invention; and

FIG. 6 presents a cross sectional view taken along line 6—6 of FIG. 5showing the inner liner flat stock plies as laid upon the tire buildingdrum.

DETAILED DESCRIPTION OF THE INVENTION

To best illustrate the present invention, FIG. 1 shows a typicalautomotive tire preform 10, in cross-section, as it exists afterexpansion of the tire preform but prior to complete vulcanization. Tirepreform generally comprises two bead areas 12 and 13, side walls 16 and17, tread or crown region 20, and an inner liner 21 having two distinctplies 24 and 25, in accordance with the present invention. For clarityof the present invention, the typical carcass reinforcing, extendingbetween bead areas 12 and 13, the belt structure in the crown area underthe tread, and the bead ring structure are not shown. The preform has aninner meridional width L extending about the interior surface 23 ofpreform 10 from the outer edge of bead area 12 to the outer edge of beadarea 13, as shown in FIG. 1.

As illustrated in FIGS. 2 and 3, the uncured inner liner 21 comprisestwo separate and distinct plies 24 and 25 of flat elastomeric materialeach having a uniform thickness and a width less than width L butgreater than one half of width L. During the tire preform buildingstage, the inner liner plies 24 and 25 are laid upon the tire buildingdrum 22, as illustrated in FIGS. 2 and 3, wherein the first ply 24extends from one edge 27 of preform width L to a predetermined position28 on drum 22 beyond the midpoint 29 of width L. The second ply 25 isapplied to the drum extending from the opposite edge 30 of preform widthL to a predetermined position on drum 22 beyond the midpoint 29 of widthL to overlap ply 24. Plies 24 and 25 are arranged to overlap one anotherby the length X. The length X will necessarily vary depending upon tiresize and the desired amount of overlap X′ in the expanded tire, as shownin FIG. 1. For clarity of the invention, the additional plies typicallyapplied to the tire preform upon the building drum 22 are not shown.

When a flat band tire preform 10 is built with the inner liner plies 24and 25 laid upon 1s the tire building drum 22, as shown in FIGS. 2 and3, and is expanded in the vulcanizing mold, plies 24 and 25, beinganchored at beads 12 and 13, respectively, will stretchcircumferentially in an amount proportional to the final diameterdivided by the diameter of the tire preform prior to expansion. Thisstretch is responsible for the reduction in the gauge of the plies 24,25. Typically, during expansion of preform tire 10, there is nosubstantial meridional, i.e. bead to bead, stretch of the plies. It ispreferred that the amount of overlap X′, after expansion of the preform,extends across crown 20 and to the breaker or shoulder regions 14 and15, as illustrated in FIG. 1.

Referring now to FIGS. 4, 5, and 6, an alternate embodiment of thepresent invention is illustrated. A typical automotive tire preform 40,in cross section, is again shown as it exists after expansion of thetire preform but prior to complete vulcanization. Tire preform 40generally comprises beads 42 and 43, side walls 46 and 47, a tread orcrown region 50, and an inner liner having three distinct plies 54, 55,and 56. For improved clarity of the present invention, the typicalcarcass reinforcement extending between the beads 42 and 43, i.e., thebelt structure in the crown area under the tread and the bead ringstructure, are not shown. The preform 40 has an inner meridional width Mextending about the inner width of surface 49 from the outer edge ofbead area 42 to the outer edge of bead area 43.

As illustrated in FIGS. 5 and 6, and in accord with the presentinvention, the tire inner liner in the uncured stage, comprises threeseparate and distinct plies 54, 55, and 56 which are shown with areduced width as compared with FIG. 4. Ply 54 has a width W which isless than inner meridional width M. Ply 55 has a width Y, typicallyequal to width W. Ply 56 has a predetermined width Z. The plies 54 and56 are generally of uniform thickness and the middle ply 56 can bethicker. With this construction, the thickness of ply 56 can be selectedso that it will be close to the thickness of plies 54 and 55 after theplies are stretched circumferentially in the vulcanizing mold. It isalso within the terms of the invention for the three plies to be of thesame thickness. During the tire preform building stage, the inner linerplies 54, 55, and 56 are laid upon the tire building drum 22, asillustrated in FIGS. 5 and 6, wherein the first ply 54 extends from oneedge 57 of preform width M to a predetermined position 58 on drum 22.The second ply 55 is applied to drum 22 extending from the opposite edge59 of preform width M to position 61. Ply 56 equally overlaps plies 54and 55 by a desired amount of overlap D and E, respectively, as shown inFIG. 4. It is preferred that the amount of overlap D and E, afterexpansion of preform 40, extends across crown 50 and to the breakerregions 44 and 45, as illustrated in FIG. 4. For clarity of theinvention the additional plies typically applied to the tire preformupon the building drum 22 are not shown.

When a flat band tire preform 40 is built with the inner liner plies 54,55 and 56 laid upon the tire building drum 22, as shown in FIGS. 5 and6, and is expanded in the vulcanizing mold, plies 54, 55 and 56 willstretch circumferentially in an amount proportional to the finaldiameter divided by the diameter of the tire preform prior to expansion.This stretch is responsible for the reduction in the gauge of the plies54, 55 and 56. Typically, during expansion of preform tire 40, there isno substantial meridional, i.e. bead to bead, stretch of the plies.

While the invention has been described in combination with embodimentsthereof, it is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art in light of theforegoing teachings. Accordingly, the invention is intended to embraceall such alternatives, modifications and variations as fall within thescope of the appended claims.

What is claimed is:
 1. In a method of building a pneumatic tire preformcomprising bead areas, sidewalls, tread region and an inner liner havinga meridional width L upon a tire building drum, the improvementcomprising applying the inner liner of elastomeric material to thebuilding drum by: applying a first ply of elastomeric material upon thebuilding drum whereby the first ply extends from one edge of preformwidth L to a first predetermined position upon the drum beyond themidpoint of preform width L; and applying a second ply of elastomericmaterial upon the building drum whereby the second ply extends from theopposite edge of the preform width L to a second predetermined positionupon the drum beyond the midpoint of preform width L and overlaps thefirst ply of elastomeric material; wherein the first ply has a widthless than preform width L; and the second ply has a width less thanpreform width L.
 2. The method of building a tire preform as set forthin claim 1 including the step of providing the first and second pliesfrom a sheet of elastomeric material having a uniform thickness.
 3. Themethod of building a tire preform as set forth in claim 1 wherein theoverlap of the second ply over first ply extends across the tread regionand to shoulder regions.
 4. A tire made by the process of claim 1.